For the protection of humans, certain safety precautions must be complied with when erecting and operating electrical devices and installations. These precautions have been laid down in national and international regulations and must be checked at regular intervals. All of them are ultimately based on measurements of insulation resistance. In practice, however, requirements differ widely; thus diverse measuring voltages and, irrespective of these, the largest possible ranges. In addition, a modern meter is expected to offer useful additional measuring functions, such as a device check after repairs and reassembly as per VDE 0701, ÖVE HG 701 and other standards. All these requirements must, however, not interfere with simplicity of operation or with the overload capacity of the instrument. The meters UNILAP ISO and UNILAP ISO X are the perfect solution. Both instruments meet the most stringent technical requirements within an area of application of maximum breadth and comply with all pertinent regulations. Their freely selectable test voltage and outstanding high ranges, together with full autoranging and GUARD technology, are eminently suitable for even the toughest measuring probFlukes, e.g. for measuring highly insulating materials. All measuring functions are fully automated under microprocessor control and indicated unequivocally and for any length of time on a large display optimized for clarity.